Testimony began Tuesday in Harrisburg, Pa., in the trial of the former East Pittsburgh police officer charged with homicide in the shooting death of Antwon Rose II.

Michael Rosfeld, 30, the white Pennsylvania police officer who shot and killed the unarmed Black teenager last year, is facing life behind bars if convicted on one count of criminal homicide.

READ MORE: 5 Things to know about Antwon Rose, the unarmed Black teen gunned down by East Pittsburgh police

Lawyers for Rosfeld were expected to argue that the June 19 shooting of Rose after a traffic stop in East Pittsburgh was justified. According to reports, the 17-year-old was riding as a passenger in an unlicensed taxicab when the back-seat passenger, Zaijuan Hester, 18, rolled down a window and shot at two men on the streets, wounding one in the abdomen.

When Rosfeld pulled over the vehicle a short time later, Rose attempted to flee and the officer shot him three times; in his face, elbow and back, NBC News reported.

Hester pleaded guilty Friday to aggravated assault and firearms violations for the incident. A judge ruled Monday that the jury of six men and six women, including three African-Americans, will hear evidence of that incident.

The last witness called Tuesday was Lashaun Livingston, who said she started recording the scene from her front porch when she became alarmed by the officer’s tone.

READ MORE: Police officer who fatally shot unarmed teen Antwon Rose identified

“That type of tone frightened me, myself,” she said. “An angry tone — harsh. It was more so angry — that he was mad at someone or something. I had a bad feeling.”

Her video shows Officer Rosfeld firing at Rose and Livingston can be heard shouting, “Why are they shooting at them? Don’t shoot at them.”

The prosecution played the short video for the jury and many courtroom spectators reportedly shook their heads in disbelief.

Livingston said she never saw the teens make any motion toward Rosfeld, and she saw no weapons.

“I had a panic attack, I couldn’t breathe,” she said, “So I hit stop [on the recording].” She testified that she later recorded again when an ambulance arrived.

READ MORE: Lawyer for officer who killed Antwon Rose demands judge recuse himself from trial

Defense attorneys maintain that Rosfeld is “very remorseful.”  They previously stated that the jury would be asked to determine if the shooting was justified.

He’s not remorseful because he’s been charged. He legitimately is sad that this happened,” defense attorney Patrick Thomassey told the Pittsburgh Post-Gazette last year. “Mike kept saying, ‘I can’t believe this happened. I can’t believe that kid didn’t have a gun in his hand.’”